1. Field of the Description
The present description relates, in general, to the illusion of stereoscopic or three dimensional (3D) image generation and/or projection, and, more particularly, to systems and methods for producing 3D or volumetric images without requiring viewers to wear 3D glasses or the like. The described devices may be thought of as providing volumetric displays or projected images that create a 3D display within a small space or container (such as a volumetric projection illusion lantern).
2. Relevant Background
There is a growing trend toward using 3D projection techniques in theatres and in home entertainment systems including video games and computer-based displays. In many conventional 3D projection techniques, the right eye and the left eye images are delivered separately to display the same scene or images from separate perspectives so that a viewer sees a three dimensional composite, e.g., certain characters or objects appear nearer than the screen and other appear farther away than the screen. Stereoscopy, stereoscopic imaging, and 3D imaging are labels for any technique capable of creating the illusion of depth in an image. Often, the illusion of depth in a photograph, movie, or other two-dimensional image is created by presenting a slightly different image to each eye or the creation of parallax. In most animated 3D projection systems, depth perception in the brain is achieved by providing two different images to the viewer's eyes representing two perspectives of the same object with a minor deviation similar to the perspectives that both eyes naturally receive in binocular vision.
The images or image frames used to produce such a 3D output are often called stereoscopic images or a stereoscopic image stream because the 3D effect is due to stereoscopic perception by the viewer. A frame is a single image at a specific point in time, and motion or animation is achieved by showing many frames per second (fps) such as 24 to 30 fps. The frames may include images or content from a live action movie filmed with two cameras or a rendered animation that is imaged or filmed with two camera locations. Stereoscopic perception results from the presentation of two horizontally offset images or frames with one or more object slightly offset to the viewer's left and right eyes, e.g., a left eye image stream and a right eye image stream of the same object. The amount of offset between the elements of left and right eye images determines the depth at which the elements are perceived in the resulting stereo image. An object appears to protrude toward the observer and away from the neutral plane or screen when the position or coordinates of the left eye image are crossed with those of the right eye image (e.g., negative parallax). In contrast, an object appears to recede or be behind the screen when the position or coordinates of the left eye image and the right image are not crossed (e.g., a positive parallax results).
Many techniques have been devised and developed for projecting stereoscopic images to achieve a 3D effect. One technique is to provide left and right eye images for a single, offset two-dimensional image and displaying them alternately, e.g., using 3D switching or similar devices. A viewer is provided with liquid crystal shuttered spectacles to view the left and the right eye images. The shuttered spectacles are synchronized with the display signal to admit a corresponding image one eye at a time. More specifically, the shutter for the right eye is opened when the right eye image is displayed and the liquid crystal shutter for the left eye is opened when the left eye image is displayed. In this way, the observer's brain merges or fuses the left and right eye images to create the perception of depth.
Another technique for providing stereoscopic viewing is the use of anaglyphs. An anaglyph is an image generally consisting of two distinctly colored, and preferably, complementary colored, images. The theory of anaglyph is the same as the technique described above in which the observer is provided separate left and right eye images, and the horizontal offset in the images provides the illusion of depth. The observer views the anaglyph consisting of two images of the same object in two different colors, such as red and blue-green, and shifted horizontally. The observer wearing anaglyph spectacles views the images through lenses of matching colors. In this manner, the observer sees, for example, only the blue-green tinted image with the blue-green lens, and only the red tinted image with the red lens, thus providing separate images to each eye. The advantages of this implementation are that the cost of anaglyph spectacles is lower than that of liquid crystal shuttered spectacles and there is no need for providing an external signal to synchronize the anaglyph spectacles.
In other 3D projection systems, the viewer may be provided glasses with appropriate polarizing filters such that the alternating right-left eye images are seen with the appropriate eye based on the displayed stereoscopic images having appropriate polarization (two images are superimposed on a screen, such as a silver screen to preserve polarization, through orthogonal polarizing filters). Other devices have been produced in which the images are provided to the viewer concurrently with a right eye image stream provided to the right eye and a left eye image stream provided to the left eye. Still other devices produce an autostereoscopic display via stereoscopic conversion from an input color image and disparity map, which typically is created based on offset right and left eye images. While these display or projection systems may differ, each typically requires a stereographic image as input in which a left eye image and a slightly offset right eye image of a single scene from offset cameras or differing perspectives are provided to create a presentation with the appearance of depth.
There is a continuous desire and need to provide new techniques that provide cost effective but eye-catching content with depth and dimension. For example, it is desirable to grab the attention of crowds in shopping malls, on busy streets, in amusement parks, and other crowded facilities such as airports and entertainment arenas. As discussed above, 3D imagery is one exciting way to appeal to viewers and hold their attention. Unfortunately, the use of 3D imagery has, in the past, been limited by a number of issues. A large draw back or hurdle is that 3D projection technologies often require the viewer to wear special viewing glasses, which is often inconvenient for many applications and can significantly add to costs.
In some projection systems, an illusion of volume or a volumetric display is created using partially reflective mirrors tilted at various angles (e.g., at 45 degrees) to a viewer's point-of-view (POV), and an image plane is produced from a projection upon a front surface of a projection screen. However, such volumetric illusion systems require several components that can require considerable set up time and present added costs. In addition, the POV of the viewer is limited. These and other limitations force these systems to be only used in larger space applications (e.g., in a large set or display). In other cases, spinning liquid crystal displays (LCDs) with media played upon them are used, but such displays are very expensive and must be spun at high revolutions per minute, which can create safety issues. Hence, there remains a need for systems and methods for providing autostereoscopic, 3D, or volumetric displays in a cost effective manner, without the need for special eye or head wear, and in small spaces such as within a container (e.g., a lantern, a jar, a small box, or the like).